Flat panel displays are found everywhere from hand held electronics to large scale video applications. Larger displays are usually smaller displays tiled together. When the displays are tiled it is important to create a bright image that appears seamless across the tiles. The image brightness is proportional to the size of the aperture ratio in the display as defined by the ratio of the emissive surface area of a pixel to the total surface area of the same pixel. Increasing the aperture ratio of the pixel produces a brighter image. However, increasing the space between pixels allows for a proportional increase in the spacing between adjacent tiles, thereby facilitating the ability to create a seamless tiled display. Therefore, any increase in the area available for each pixel can be distributed optimally to increase the aperture ratio, and to increase the space available between pixels including the space between adjacent pixels on abutting tiles.
Flat panel technology has been dominated by liquid crystal displays (LCD's) in which the liquid crystal material, when activated by an electric field, acts as a valve to transmit light from a back light source. LCD's require a transparent path that includes a transparent substrate and transparent pixel electrodes. There cannot be anything blocking the pixel from the backlight. In video LCD displays the space available for creating seams between tiles is limited by the rows of circuits that fill the space between pixels.
U.S. Pat. No. 5,056,893 describes a technique in which there is increased space for a seam by making the pixels at the edge of a tile smaller. Reducing the size of the pixels is a significant trade-off in brightness and image quality. U.S. Pat. No. 5,903,328 describes tiled LCD displays where the adjacent tile edges are ground at an angle and overlap each other. This allows a small increase in the space for the ground edge relative to the adjacent pixels; however, as the space increases the distance between the image planes of adjacent tiles increases proportionally. U.S. Pat. No. 6,136,621 describes a method for making a high aspect ratio gated emitter wherein the lower gate is partially covered by an insulator and the upper gate; the lower gate extends through a hole in the insulator and the upper gate. U.S. Pat. No. 5,955,744 describes a LCD display wherein the TFT is under the pixel electrode, located just outside the perimeter of the pixel so as not to block light from the backlight.
Emissive displays, which produce their own light, do not require a transparent substrate. The pixels do not have to be positioned over a transparent substrate or a transparent electrode. This allows for stacking of the integrated drive circuits and the circuits under the light-emitting layer which contains only an array of light-emitting pixels. These tiles can be arrayed together to make a monolithic tiled display wherein the pixel pitch across the seam of adjacent tiles is substantially equal to that of the pixel pitch within a tile. In order to achieve an emissive device with high aspect ratio pixels, the pixels on each tile are addressed through vertical connections and a conductor layer to the corresponding circuits. The drive circuits are semiconductor electronics that are manufactured directly on the substrate and can be on the same level as the circuits or under the circuits. The drive circuits can also be located on the bottom side of the substrate and connected using vertically connections through the substrate. U.S. Pat. No. 6,091,194 describes an emissive display tile in which discrete drive circuits are attached to the bottom side of the tile.